There are many foodstuffs that are susceptible to contamination by mold and bacteria and products thereof. For example, grains and feeds that have been exposed to warm humid atmospheres can become contaminated by aflatoxins. Aflatoxins are highly toxic carcinogenic substances produced by the naturally occurring molds Aspergillus flavus and Asgergillus parasiticus. Unless the affected material is de-toxified, the aflatoxins can cause severe damage and death to animals or humans who ingest the affected foodstuffs. Hence, there is an ongoing need for economical processes for de-toxifying aflatoxin contaminated agricultural products intended for human or animal consumption.
A number of techniques have already been developed for de-toxifying aflatoxin contaminated foodstuffs. The following patents and article are incorporated herein by reference and describe the results set forth below by way of example.
In U.S. Pat. No. 2,641,542, Ulrey describes de-toxification of tung meal by treatment with anhydrous ammonia or amines at a temperature typically in the range of 200.degree.-250.degree. F. at a pressure of about 4 atmospheres for a period of 30-60 min. Below these temperatures and pressures the reaction is too slow to be useful. Ulrey states that it is not necessary to wet the meal or separate the reaction products.
In U.S. Pat. No. 3,429,709, Masri et al., describe de-toxification of agricultural products contaminated with aflatoxins by mixing in at least 0.3 gms and preferably 10-30 gms of NH.sub.3 per kilogram of foodstuff and heating to 20.degree.-121.degree. C. for times ranging from 7-14 days at the lower temperatures to 30-60 minutes at 121.degree. C. Masri found that it was desirable that 10-15 % moisture be present during de-toxification either as liquid or steam since it increased the rate and degree of de-toxification. For ammonia in gaseous form, Masri et al. pressurized the treatment chamber to 5-40 psig with the gas. After treatment, the ammonia was removed from the material by evacuation or by purging with air or nitrogen or other inert gas. When moisture had been added, a post treatment drying step was also used.
In U.S. Pat. No. 3,585,041, Mann et al., describe de-toxification of peanut meal contaminated with aflatoxins by mixing the meal with methyl amine in a closed vessel at atmospheric pressure and a temperature of about 75.degree.-100.degree. C. for times of an hour to a Week. The amine was then removed and the meal dried. If the moisture content of the meal was below about 7 %, water was added before treatment.
In U.S. Pat. No. 3,890,452, Brandt et al., disclose a method of reducing the aflatoxin content of contaminated oilseed meal by combining the meal with water, at least one oxide and/or hydroxide of an alkali metal or alkaline earth metal, and at least one organic amine. The mixture must have a pH of at least 8, preferably 9.5 or higher. The mixture is reacted at a temperature of 70.degree.-150.degree. C. for time ranging from 10 minutes to 15 days at atmospheric pressure or above, and then dried. The higher the temperature and pressure the shorter the required treatment time.
In U.S. Pat. No. 3,919,432, Elliger et al., describe a method for reducing the aflatoxin contamination of jojoba meal by storing the meal in a closed container in contact with 5-10% by weight of ammonia, e.g., as ammonium hydroxide or as gas, for 25-35 days. The meal should contain 20-25% water by weight.
In U.S. Pat. No. 4,035,518, Carmona describes a method for obtaining aflatoxin free foodstuffs, such as whole grains, seeds, or kernel nuts by exposing the foodstuffs to a weakly alkaline aqueous solution for a short period of time (e.g., 5-15 min. at 180.degree.-213.degree. F.), washing with water to a neutral pH and then picking out the aflatoxin contaminated grains or kernels which become colored as a result of the treatment.
In U.S. Pat. Nos. 4,421,774, 4,338,343, 4,335,148 and 4.350,709, Vidal et al., teach various methods for detoxification and preservation of grain by perfusion with (i) sulfur dioxide gas bubbled through an organic acid such as propionic acid, followed by or combined with (ii) ammonia gas perfusion.
In U.S. Pat. No. 4,450,178, Korsgaard discloses a method for supplying ammonia to baled straw to reduce aflatoxin contamination therein. The ammonia is supplied in gaseous form through hollow tines used for handling the bale.
De-toxification of aflatoxin contaminated agricultural products by ammoniation and other methods has also been extensively discussed in the technical literature. The article by D. L. Park et al., entitled "Review of the Decontamination of Aflatoxins by Ammoniation: Current Status and Regulation", J. Assoc. Off. Anal. Chem (Vol. 71, No. 4, 1988), pp. 685-703 is noteworthy. Some of the results reported by Park et al., are summarized in Table I below.
Despite the many years of intense effort by researchers throughout the world, the processes available for de-toxification of foodstuffs contaminated with aflatoxins and the like are far from ideal. For example, those processes that are effective at atmospheric pressure and low temperatures usually take unduly long times; processes that have short processing times usually require higher temperatures and/or pressures and more expensive treatment chambers; and processes that provide rapid processing at low temperatures and atmospheric pressure usually require expensive materials or post-treatment steps.
Table I following, shows a summary of reported data, according to Park et al., ibid., for various foodstuffs treated with ammonia or ammonia compounds at pressures of 1-3 atmospheres and at temperatures in the range of 10.degree.-145.degree. C. for time periods of 0.25-1008 hours and for various moisture contents. The numbers shown in parentheses following the foodstuff name refer to the citations in Park et al., ibid. The entries "AT" in the temperature column refer to "Ambient Temperature" and the entries "ND" in the final aflatoxin level column refer to "none detected" or the like.
TABLE I __________________________________________________________________________ AFLATOXIN LEVELS IN PPB IN FOODSTUFFS TREATED AT 1-3 ATMOSPHERE WITH THE INDICATED TEMPERATURES AND TIMES MOIST. TEMP. TIME AFLATOXIN LEVELS DE-TOXIFICATION FOODSTUFF (%) .degree.C. (HRS) INITIAL FINAL MATERIAL __________________________________________________________________________ TREATMENT AT ATMOSPHERIC PRESSURE PEANUT MEAL (67) 30 100 2 111 10 NH4CO3 + NaOH CORN (68, 69) 17.5 10 1008 1000 &lt;20 1.5% AMMONIA " " 25 192 " " " " " 40 48 " " " " 12-17.5 25 288 180 ND " CORN (70) 15 25 504 600 &lt;20 AMMONIA " " 38 72 " " " " 17.5 AT 312 750 &lt;5 1.5% AMMONIA PEANUT MEAL (81) 20 AT 240 2500 &lt;25 5% AMMONIA PEANUT MEAL (82, 83) 15 AT 120 970 450-413 3-5% AMMONIA " " 50 120 " 34-21 3-5% AMMONIA PEANUT MEAL (84) 20 AT 240 (79% REDUCTION) 5% AMMONIA MAIZE (84) " AT 240 (97% REDUCTION) " COTTON SEED (85-87) 20 AT 504 1500-1900 55 1.5% NH4OH COTTON SEED (88) 7.5 43 240 800 &lt;20 2.0% AMMONIA " 7.5 21-43 360 " " " " 20 43 360 " " " CORN (65) 20 145 3 270 3 0.5% AMMONIA PEANUT MEAL (5) 15-20 100 1 (95% REDUCTION) 7% NH3 @ 1 ATM TREATMENT ABOVE ATMOSPHERIC PRESSURE PEANUT MEAL (92) 17 118 1 1977 32 4% NH3 @ 26 PSIG (92) " 124 0.5 " 112 4% NH3 @ 27 PSIG (92) " 100 2.5 1000 50-240 3% NH3 @ 5 PSIG CAKES/MEALS (50-53) 15 95 0.5 600 ND DRY NH3 @ 3 BARS COTTON SD. ML. (60) 14 100 0.5 4000 &lt;4 4% NH3 @ 40 PSIG COTTON SD. ML. (57) 10 82 0.5 425 ND 4% NH3 @ 30 PSIG PEANUT MEAL (60) ? 80 0.25 1148-1530 32-75 NH3 GAS @ 3 BARS PEANUT MEAL (64) ? 80 0.25 980-1140 30-60 NH3 GAS @ 3 BARS COTTON SD. ML. (48) 15 93 0.5 334 3 DRY NH3 @ 45 PSIG __________________________________________________________________________
In the experiments summarized in Table I, significant reduction in aflatoxin contamination levels was observed. But, it is also apparent from the data in Table I that aflatoxin de-toxification times of many hours are required using prior art methods with ammonia or ammonia compounds unless the foodstuff-ammonia mixture is heated to at least about 100.degree. C. and/or the pressure raised to several atmospheres during de-toxification. It is expensive to supply heat and/or pressure to the foodstuff-de-toxicant mixture. Hence, these prior art measures are less desirable.
A further difficulty with some prior art de-toxification treatments is the tendency for aflatoxin levels to recover or rebound after the de-toxification. This is referred to in the art as "reformation". Reformation apparently occurs naturally and is accelerated by exposing de-toxified materials to neutral or acidic conditions, such as may be encountered during storage or in animal or human digestive tracts. Thus, if the storage or digestive period is prolonged, foodstuffs that appear to have acceptably low levels of aflatoxin after decontamination, may recover during storage or digestion to potentially harmful aflatoxin levels. Thus, a further measure of the effectiveness of a de-toxification method is the amount of aflatoxin reformation that is encountered after de-toxification, particularly after exposure to acid environments.
It has been found that materials de-toxified using the least expensive prior art techniques such as those employing the shortest treatment times and lowest temperatures and which operate at atmospheric pressure, are more prone to significant reformation. This is a substantial disadvantage of such prior art methods.
Thus, none of the prior art processes is completely satisfactory, and there is a continuing need for improved methods of treating agricultural products contaminated with aflatoxins and the like.